1. Field of the Invention
The present invention relates to a toner capable of achieving energy saving and high quality performance in image forming techniques using an electrophotographic process, such as copiers, laser printers, and facsimiles, and also relates to a method for producing the toner.
2. Description of the Related Art
In image formation through an electrophotographic process, generally, an image is formed using a toner on a print medium such as paper, and then the print medium is heated while being pressurized by a fixing member such as a fixing roller, thereby a final printed matter is obtained. Meanwhile, in environmental problems needing technological solutions, in recent years, apparatus and devices are required to reduce energy consumption. However, in electrophotographic processes, a large amount of energy is consumed in heating in the fixing process, and thus there is a demand to decrease the temperature necessary for the fixing.
As one of measures to decrease the fixing temperature, it is known to reduce the molecular weight and the glass transition temperature of a binder resin constituting a toner so as to melt the binder resin at low temperature. However, when the heating temperature exceeds the glass transition temperature of a resin, the viscosity of the resin gradually decreases as the temperature increases, and thus in order to decrease the temperature necessary for fixing an image on paper or the like, there is a need to design a resin used so as to have a lower molecular weight to some extent and have a low glass transition temperature. When the resin is designed to an extreme, the resulting toner itself causes blocking during storage, splits, deformation and adhesion to various members in developing and/or transfer processes, and as a result, the quality of print images is significantly impaired. For this reason, there is a limitation on this measure. To solve this problem, there is proposed a method in which a crystalline material is added to a toner to be compatible with a binder resin in a fixing process and to reduce the melt-viscosity of the toner, and thereby an image is fixed at a low temperature (see Japanese Patent Application Laid-Open (JP-A) No. 2007-233169).
This proposal disclosed, for the purpose of proposing a toner which is usable in a low-temperature fixing system, has excellent offset resistance, and is capable of forming a high-quality image excellent in image sharpness for a long period of time, without smearing a fixing device and the formed image, a developer using the toner, a toner container, a process cartridge, an image forming apparatus and an image forming method, to make a fixing auxiliary compatible with a polyester resin having a melting point of 50° C. or higher but lower than 150° C. present in the toner in a crystalline phase domain. However, in the course of the production processes, part of the crystalline material is compatible with the binder resin, and thus this technique has a problem that the storage stability of the toner degrades, and the toner is deformed in developing and transferring processes and easily adheres to various members.
Further, Japanese Patent (JP-B) No. 3678060 disclosed a toner containing a crystalline material and a styrene acrylic resin. In the toner described in JP-B No. 3678060, the styrene acrylic resin, which is an amorphous polymer, and the crystalline polyester greatly differ in skeleton and is hardly compatible with each other, and thus each of these materials can be present in an independent state. However, the toner has a problem in that the probability of low temperature fixing is low because of poor compatibility of these materials.
Furthermore, Japanese Patent (JP-B) No. 4275391 describes a technique of using a crystalline polyester and an amorphous polyester, as a binder resin, in a compatible state. In this case, however, the glass transition temperature and toughness of the binder resin as a whole degrade, and thus the toner has a problem with its poor storage stability.
In conventional toners containing crystalline materials as described above, the crystalline material which is added to decrease the melt viscosity of the resulting toner is compatible with a binder resin, and part of the crystalline material is soluble in the binder resin in production processes, resulting in a decrease in the glass transition temperature of the entire system of the toner. Accordingly, such conventional toners have problems in that due to the decrease in the glass transition temperature, the resulting toner undergoes degradation of storage stability, deformation in developing and transferring processes, and adhesion to various members, with ease.